This invention relates to a brake actuator for delivering a brake force through a brake block or brake pad to a wheel or disc to be braked, the actuator comprising in a housing a service brake arrangement.
Brake actuators for service braking of vehicles, both rail vehicles and automotive vehicles, are well known. Such actuators are normally pneumatically or hydraulically operated, but also electro-mechanical actuators are known. Service braking of a vehicle may occur as block braking or disc braking, as is well known in the art.
It is in many cases desirable that the vehicle is braked if the supply of the normal brake medium, normally the pneumatic or hydraulic pressure, fails. The normal way of achieving this is by means of a so called spring brake, in which a powerful compression spring is held compressed and inactive by means of pneumatic or hydraulic pressure in a separate chamber; if this pressure drops for any reason the spring will expand and accomplish spring braking.
In certain cases, however, a normal spring brake is not the right solution. Especially if the service brake is of the electro-mechanical type, such a spring brake is not applicable at all.
A brake actuator of the kind defined above, fulfilling all requirements and specifications, is according to the invention attained in that the actuator also comprises a safety brake arrangement including at least one powerful spring, acting in the brake application direction, means for tensioning the spring by the reaction force at a service brake application, and mechanical means for locking the spring to the housing in a tensioned state, which locking means can be released at will for accomplishing a safety brake application.
It will be noted that in this solution still a powerful spring (or several powerful springs) is used for the safety brake. However, this spring is tensioned at the first service brake application after former use and is mechanically locked in this tensioned state, until it is to be used for safety braking, when for example electrical control power to the locking means is cut off.
In a first practical embodiment of the invention, in which the service brake arrangement is actuated by a pressurized brake fluidum, preferably compressed air, an inlet for the brake fluidum is arranged between a service brake piston and a safety brake piston, the safety brake spring being arranged between the safety brake piston and the actuator housing, and releasable locking means are arranged in the housing for releasably holding the safety brake piston.
In this arrangement the two brake pistons are pressed apart at a first application by the brake fluidum, and the safety brake piston is mechanically locked to the housing with the safety brake spring compressed and ready for action, whereupon normal service braking can occur without any interference with the safety brake arrangement.
In this embodiment a locking rod may be rotatably journalled to the safety brake piston and be in thread engagement with the housing, and means can be provided to releasably lock the locking rod to the housing.
Preferably the locking means include an electro-magnet attached in the housing and a locking washer, which is connected to the locking rod and is arranged in the vicinity of the electro-magnet for locking thereby.
In a specific variation hereof a locking spring is arranged between the locking washer and the locking rod for obtaining a locking servo action.
In another version of the locking means a connecting spring ring is arranged in corresponding grooves in a tubular piston rod of the safety brake piston and a sleeve or extension in the housing, and control means are provided on the housing for changing the diameter of the spring ring between positions for engagement and disengagement between the piston rod and the housing extension.
In a second practical embodiment of the invention, in which the service brake arrangement still is actuated by a pressurized brake fluidum, the safety brake spring is arranged between the housing and a safety brake piston, which is placed in front of the service brake piston as counted in the brake application direction and is provided with attachments extending out through slits in the housing, and releasable locking means are provided between the housing and a tubular safety brake piston, which encloses a push rod for the service brake.
This embodiment is rather close to the previous embodiment in certain respects. However, the safety brake arrangement is arranged in front of the service brake arrangement, and attachments on the safety brake piston serve as mountings for the actuator in the vehicle.
The locking means in this embodiment preferably consist of a connecting spring ring, which is arranged in corresponding grooves in a sleeve-shaped housing extension and the safety brake piston rod, and the control means are provided on the housing for changing the diameter of the spring ring between positions for engagement and disengagement between the extension and the piston rod.
The control means hereby include an electro-magnet, a pneumatic or hydraulic actuator or the like.
In a third embodiment of the invention, in which the service brake arrangement is actuated by a pressurized brake fluidum, preferably hydraulic fluid acting on a service brake piston, at least one safety brake spring is arrangedxe2x80x94in a disc brake caliper, generally comprising a caliper frame and a caliper housingxe2x80x94between a caliper frame flange and a caliper housing flange, and a locking rod is rotatably journalled in the caliper frame and is in thread engagement with the caliper housing, means being provided to releasably lock the locking rod to the caliper housing.
The locking means here preferably include an electro-magnet attached in the caliper housing and a locking washer, which is connected to the locking rod and is arranged in the vicinity of the electro-magnet for locking thereby.
In a fourth practical embodiment, in which the service brake arrangement is actuated by an electric motor via means for transforming its rotary movement into an axial movement of a service brake push rod, i.e. an electro-mechanical service brake, the safety brake spring is arranged between the housing and a safety brake piston, which is provided with attachments extending out through slits in the housing, and releasably locking means are provided between the housing and a tubular safety brake piston rod, which encloses the service brake push rod.
Here, a connecting spring ring is arranged between a sleeve shaped housing extension and the safety brake piston rod, and control means are provided on the housing for changing the diameter of the spring ring between positions for engagement and disengagement between the housing extension and the piston rod.
Also in a fifth embodiment the service brake arrangement is actuated by an electric motor via means for transforming its rotary movement into an axial movement of a service brake push rod or force transmitting member. Accordingly, this arrangement is an electro-mechanical service brake, and in fact this is a practical and preferred embodiment.
Here, in a disc brake caliper, generally comprising a caliper frame and a caliper housing, at least one safety brake spring is arranged between a caliper frame flange and a caliper housing flange; a locking rod is further rotatably journalled in the caliper frame and is in thread engagement with the caliper housing, and means are provided to releasably lock the locking rod to the caliper housing.
These locking means may preferably include an electro-magnet attached in the caliper housing and a locking washer, which is connected to the locking rod and is arranged in the vicinity of the electro-magnet for locking thereby.
In one modification hereof a locking spring is arranged between the locking washer and the locking rod for obtaining a locking servo action. This locking spring may constitute a slitted end portion of the locking rod.